cw1200: Fix suspend

The cw1200 driver implements suspend and resume callbacks and assigns them
to the suspend and resume fields of the device_driver struct. These
callbacks are never actually called by anything though.

Modify the driver to properly use dev_pm_ops so that the suspend function
is actually executed upon suspend and drop the empty resume function.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>